| This research examines factors that influence biofiltration of landfill gas, prior to energy-recovery processes. Although gas-to-energy projects have many benefits to public health and potential climate change effects, chlorinated vapors in the gas can harm energy recovery equipment. Three characteristics of landfill gas could impact the effectiveness of a biofilter in removing the chlorinated substituents: low oxygen, high carbon dioxide, and high methane concentrations. A compound found in landfill gas emissions, 1,2-dichloro-ethane (1,2-DCA), was selected as the target of dechlorination studies using a well-characterized bacterial strain, Xanthobacter autotrophicus GJ10.; Changes in removal efficiency due to varied levels of oxygen were demonstrated in a continuous flow, gas-phase, packed column biofilter. The biofilter retained 80% of its removal efficiency when oxygen was decreased to between 2 and 5%, for a loading rate of 1.2 or 2.4 mmol 1,2-DCA/m3/min. Transformation of 1,2-DCA was sharply curtailed under oxygen concentrations less than 0.5%. Batch tests provided evidence that X. autotrophicus GJ10 can also dechlorinate 1,2-DCA after oxygen is removed, although at a rate approximately one-third of the transformation rate observed under optimal conditions.; Batch experiments showed that high concentrations of methane or carbon dioxide (when pH was controlled at 6.2) did not inhibit the growth rate of X. autotrophicus GJ10 or the transformation rate of 1,2-DCA. In the absence of sufficient buffering, however, carbon dioxide is expected to dramatically lower pH values. In tests over a range of pH from 3.6 to 7.0, growth rates for pH ≥5.6 were similar. However, transformation rates were decreased by approximately 25% at pH = 5.5, compared to observed rates at pH = 7.0.; This research indicates that biofiltration could be a feasible pretreatment for gas streams with aerobically biodegradable constituents. Significant effects of pH can be ameliorated with proper buffering from either the packing material or added liquid media. Removal of chlorine substituents can be obtained while maintaining an oxygen concentration of less than 5% in the gas. A low oxygen content has important benefits in safety and in thermal value of the treated gas stream. |
